Technology.Life.Insight.

I take a lot of time off during the holidays so decided this was the year to finally build the tree house my kids have been asking for… or fort, or tree fort, or whatever you’d like to call it. It does seem that a structure of this sort should have something to do with a tree, either in or around one, preferably. I have 2 dozen very tall and mature trees on my property, sadly none suitable to hold the base of the house (without building a scaffolding to work on). I’m also not a fan of driving bolts into a living tree, so I opted to build a raised structure to go around a tree instead.

After a while I lost track of how much time I spent on this. As a consummate homebody I take on a lot of projects and DIY efforts, so basically whenever I felt like it, I just went outside and worked on this thing. No rush, so I took my time and had fun doing this, 95% by myself. From a materials standpoint, this cost me under $1000. I’m documenting this here selfishly to catalogue the experience but hopefully there is something here to may be helpful to you if you endeavor to take on a project like this.

Planning

It is possible to spend considerable effort in the planning stages: drawing plans, creating 3D models in Google SketchUp or detailed blueprints in Visio. I considered all 3 options but went with the old-fashioned map pencils + paper route in the end. Don’t ask why, Visio would have worked better but alas it got the job done… As long as you establish some solid guiding structural measurements and work within those confines, you’ll be fine. This is a tree house after all, not a house for your mother.

First I started by staking out the ground I intended to build on. Stake nails + twine to visualize the area consumed by the structure I endeavored to build. I knew I wanted to build a rectangular deck with a play house in the corner. 10x12 overall is the largest I could go without requiring a permit from the city. If you do this, you might consider putting a call into your local building department to check as well. Once the basic footprint was decided I drew out the basic layout and started planning for the cut list.

I did a lot of reading about deck building and load considerations. Part of the challenge here was that I definitely did not want to dig 8 holes and set posts in concrete, so I knew for sure that I wanted to use pre-formed concrete footings. The catch with these is that the largest post they support is a 4x4. Reading through deck building standards that speak to load per square foot, the post size load capabilities based on height, span of the footings etc… quagmire and really overkill for a tree house. I settled on the corners, centers of 12-foot sides and added extra supports in the center in front of the tree. This should be more than adequate for this job.

Tools I used in this project:

Miter saw

Circular hand saw

Jig saw

Tape measure

Carpenters square

Cordless drill for Phillips screws

Corded drill for drill bits

Drill bits of various sizes

Soft clamps

Ratchet set for lags

Pliers

Torpedo and 48” level

The Deck

Plotting this out gave me the basic info I needed to build a cut list for the deck. I compared prices between Home Depot and Lowes online which varied, but I found in the local stores that the prices were identical. I also found that Lowes had higher quality lumber, generally speaking, with straighter boards and longer more generous cuts…but I sourced lumber from both places ultimately. Most of the better wood is in the back of the pile so it’s worth the effort to dig a bit to find the good stuff. I undershot on the supports and posts originally and ended up needing a few other pieces as well, but my original estimate was pretty close.

7 x concrete footing blocks - $50

4 x 4x4x8 pressure treated - $40

2 x 2x8x10 - $23

5 x 2x8x12 - $50

24 x 5/4x6x10 - $130

3 x 2x6x8 - $15

5 lbs 2.5" galvanized exterior screws (primeguard) $30

2.5” galvanized deck nails (with the ridges) $15

28 x 4"x3/8” lag screws + washers $10

joist hangers $10

Actual cost of deck: ~$400

First step was placing and leveling the supports. Measuring from the corners and placing those first worked best, leveling all 4 sides of each support. One of the challenges I had here was that I’m building on a slight slope. I built 3 sides of the 2x8 frame box on the ground getting each corner as square as possible and secured with 4x3/8” lags. Next was attaching the 2 corners and middle posts on the ground so I could flip it over and navigate the structure around the tree. I had a big partially supported “C” at this point. Once in the final position I added the other end of the frame and secured the remaining posts. In the pic below you can see that I almost got the footing placements right with one outlier. I also had to move the back beam up a bit to get it level on account of the slope. (Apologies for the quality of some of these pics. Low light + low battery + experimental camera app = lines)

With the basic frame in place I could start measuring and placing joists. I installed the 2x8’s with 24” between them and used properly sized joist hangers. The nails I used were slightly too long at 3” regrettably, 2.5” would have worked better. Something to consider and plan for since you don’t want improperly sized nails popping out of your deck frame. The alternate approach here is to use lags to secure the joists from outside in. Hangers do make it easier but you have to be careful with the measurements, cuts, and angles at which the nails will pass through the wood. I also built a framed box around the tree opening since the run of one of the joists was interrupted by the tree.

With the base structure completed I could now begin placing the 5/4” floor boards. Buying straight boards is especially important here as one bendy board will throw off every other board that follows. Some of this is inevitable and I certainly had my fair share of spaces with a little extra over hang on the final board. These boards can be installed long and cut off with a circular saw on the deck or cut to length before installation. The deck saw cutting method can be tricky depending on how close to the frame you want to be and where the lag heads are.

With the deck floor complete I moved on to the ladder. The ladder is fairly easy to eye-ball the angle and cut to fit the deck. Get one stringer right then duplicate it. I went on total gut feel and eye-balling for this and it turned out fine. Take a 2x6 stringer board, lay it against the deck and determine the angle you want. Draw a straight line down the face of the stringer to match the face of the deck frame. Cut that line, check the fitment, then do the same on the ground side. You should end up with a stringer that is 95% flush on the deck side and flat on the ground.

You will want some kind of solid stone support beneath the feet of the ladder; I buried 2 old bricks for this purpose. The steps of the ladder were a little trickier and I built the first few on the ground. 6.5”-7” of rise is common for a natural stair climb with no tripping. I checked the staircase in my house just to be sure and modeled after that. Measure out each step, mark, level the step and secure it into place on both sides. I used 6 x 3” nails per step and it’s solid as a rock. Screws do not work well for this! I may come back and add extra supports under each step but so far it’s holding fine. I secured the ladder to the deck via screws in the front and lags through the back. I cut a wood stake out of some scrap 2x8, pounded it into the ground by the ladder and screwed it to the stringer for extra support. Just as a side note, if you want to make this more staircase like, the DIY store sells pre-cut stringers. Just add the steps and nail it all together.

The House

For the house I planned a 6x6 foot structure, 5-feet high, with a pitched roof netting 7 feet at the peek. I drew out the walls with the planned measurements and estimated my cut list. I tried to be as efficient as possible to minimize waste and save money by buying boards that could be cut in half if possible. Efficiency was a little harder to achieve on the siding than I would have hoped.

Tree house supply list:

4 - 2x4x12 ($20)

10 - 2x4x10 ($50

6 - 2x4x8 ($20)

50 - 5/4x6x8 ($90)

3 - 5/4x6x10 ($15)

Actual cost of house: ~$350

The first step was building the walls. 5x5ft on the sides and 5x6-ft across the back, taking into account the 7” (total) consumed by the side walls. I built the walls on the deck trying to carefully pre-drill and square all corners as I went along. I spaced the interior studs at 22” but wished I shortened them a bit as I could have made more use of the scrap siding I had. Something else to be careful of here is to ensure that the window opening is spaced evenly so the siding will cover the top and bottom sills without having to cut a notch. I had it planned this way originally but foolishly changed the measurements at the last minute for some reason.

I built the 3 walls first then assembled them on the deck, the back wall between the sides. I secured them to the deck using screws and a lag in each corner screwing into a 4x4 post below. Hopefully this will be sufficient.

For the front wall, I measured out 30” for the door, framed and centered it. Next up the siding. I started on the back wall then layered in the sides. Again, very important to have straight boards here, one off causes a domino effect. Stacking up the sides around the windows is tricky for this very reason. By the time I got to the top again where a single board was needed, one side would be slightly different than the other leaving a small gap.

I finished up most of the siding then started on the rafters. I was short a few boards on the last side but made due moving forward until I made another lumber run.

Rafter Framing

The pitched roof was the single most difficult part of this project. I had to learn some new math which was fun but the rafter assembly was not. I decided to build a very typical 6/12 pitch roof which means 6” of rise for every 12” of run. This is where the carpenters square plays an especially important role as it is used to identify the proper angles for cutting. Lining up the 6 and 12 on the outer edge of the carpenters square will expose the plumb line that needs to be cut as well as the seat cut which sits on the walls. Plumb line = the angled cut at the top and bottom of the rafter.

This angle also happens to be 26.5-degrees on the miter saw as you can see here with the pencil line from the square next to the saw blade shadow.

The next part of the rafter cut is the bird’s mouth or seat cut which is where the rafter will sit on the wall plate. A construction calculator can help make figuring out the lengths required much easier but honestly the only part I really needed it for was the diagonal measurement. There app IOS/Android apps for this if interested. Knowing the right measurements + the aid of the square to identify the angles yielded precise rafters. The good folks at This is Carpentry have a very good tutorial on this process so I won’t bore you with the details here. With one rafter cut properly, I used it as a template for the others and used a jig saw for the seat cuts. As you can see here the rafter seat cut is supposed to go over the external sheathing. 4” wall plate = 4” seat cut as a good practice. Overhang is adjustable to your liking, I went with a standard 6”.

I took a design queue from my shed, which is a framed structured as well, where the builders secured the rafters to the walls using additional 2x4s on top of the wall plates. You can use metal hangers to secure the rafters to the wall or do it this way. Screw down a 2x4 cut to fit between one rafter section, screw or nail the rafter into the 2x4 from the side and secure the corner rafters from the outside in. Simple, clean, and secure.

With the rafters assembled and secured to the house I could start thinking about the roof.

Before starting on the roof, I finished siding the front/ back and put a decorative trim piece on the face.

I debated long and hard what to do about the roof. Tin, wood, shingles, lapped… There really aren’t too many viable options. I ultimately went with simple cedar planks, same as the sides, which are no where near water tight but with pressure treated wood + cedar I’m not worried. We had a 3-day rain soaker and the entire structure was dry in a day.

You want as few holes as possible when doing planks on the roof like this so I used 3 screws per board. Hopefully that will be sufficient. I started at the peak and worked down each side, trying to keep the boards as straight as possible. It turned out ok!

Next steps are doors, shutters, and a railing perhaps. I might also figure out something along the lines of a monkey rope swing. I might also put a few more knee-braces on the deck posts for added stability although this thing is pretty solid as is. I’ll update this post with the door etc as it comes along but for now this tree house is ready for action. So far I know it can hold ~500-600 lbs of kids and adults with no issues. In the end I have a better built, higher quality structure than the pre-assembled kits for a fraction of the price. What you see above netted a total of ~$1000 with 3-4 weeks of my time. I enjoyed this project a lot and didn’t mind either investment. :-)

Considerations/ lessons learned:

Screws will work for the majority of the project but for some things nails just work better: namely ladder steps and rafters.

Level, level, level. Everything at every step (besides the roof) should be level.

A speed square is highly recommended but some kind of carpenters square is a must. Don’t assume that 2 flat pieces of wood in a corner will be square. Make sure or be sorry later!

Pre-drill every hole for nails or screws to avoid splitting. Tedious but worth it.

Duplicity of tools can be a good thing when doing a project like this. 2 tape measures, 1 for your miter saw, 1 for the measurements you make on the deck, two drills one for your drill bit 1 for your screws, 2 pencils, one for the tree house, one for the saw…

PT pine posts will split (check) which is perfectly normal and part of the drying process. The more expensive cedar posts won’t do this if you want to upgrade your lumber.

Always buy 1-2 more of each board type. Sh!t happens and you will likely need extras.

When installing the rafters, make sure to get the corners as close to the front and back wall edges as possible. Siding will attach to these so needs to be as close to flush as you can get it.

When putting on the roof boards, measure down each rafter to ensure proper alignment. Domino affect if one is off…

Cedar + pressure treated wood = beauty and long life. Rain dries quickly if well ventilated.

5lbs of screws turned out to not be enough. 10lbs total is more realistic.

Sources of inspiration:

The Handmade Home - AWESOME multi-part blog on their tree house build. I took a lot of tactical queues from here.

5 comments:

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